1. Field of the Invention
The invention relates to a method of treatment of mineral oils or their distillation residues by hydrogenation, particularly so-called waste oils contaminated with halogenated hydrocarbons such as chlorinated biphenyls, brominated biphenyls, chlorinated naphthalenes, chlorinated terphenyls, other chlorinated aromatics, chlorinated paraffins, and/or chlorinated napthenes (chlorinated cycloparaffins).
2. Discussion of the Background
Among the chlorinated hydrocarbons, an urgent need exists for a safe method of disposing of the polychlorinated biphenyls (PCB's). These compounds have been made subject to maximum allowable concentration standards in the workplace, for example, of 0.5-1.0 mg/m.sup.3 (depending on chlorine content which concentrations have been quoted as maximum limits in the F.R. of Germany), as well as stringent government regulations relating to their manufacture and use. Because of their thermal and chemical stability and their dielectric properties, they have been employed as insulating and cooling fluids in high-current capacitors, transformers, and rectifiers; as plasticizers for paints, varnishes, and plastics; as impregnating fluids in packings and seal liquids in liquid seals; as hydraulic oils; and as heat transfer media (see "Roempps Chemielexikon", 8th Ed. p. 715).
Due to the low environmental degradability of chlorinated biphenyls and other related chlorinated hydrocarbons, there is a need for safe means of disposing of them on an industrial scale.
In particular, PCB-containing liquids and used PCB-containing liquids mixed into oil residues must be regarded as hazardous waste, which must be identified, specially treated, and safely stored and/or disposed of.
A number of methods of treating chlorinated biphenyls for disposal purposes have been developed. These include methods of thermal incineration, adsorption, solvent extraction, catalytic treatment with hydrogen in the presence of organic solvents, chlorolysis treatment with chlorine in the vapor phase, dehalogenation by sodium or organosodium compounds, microwave plasma treatment, ozonation, reaction in the presence of oxygen with a reagent prepared from sodium metal and polyethylene glycols, cleavage of the PCB molecule into biphenyl and chlorine, and direct oxidation of chlorinated biphenyls by air or oxygen in an aqueous phase in the presence of acids at high temperatures (see Ackerman, D. G., et al., 1983, "Destruction and disposal of PCBs by thermal and nonthermal methods", Noyes Data Corp., Park Ridge, N.J.).
None of the above-mentioned methods can be considered as suitable and unconditionally applicable for all application situations. Thus, the thermal incineration methods require extensive precautionary means for monitoring and possible post-treating of the flue gases generated, as well as treatment and disposition of solid residues which may be produced. Nonetheless, these methods are the most highly developed and most widely used. Some of the other methods are only at the bench or pilot stage of development.
As an example, see the research report of Kranich, W. L., et al., 1977, "Process for hydrodechlorination of polychlorinated hydrocarbons", Am. Chem. Soc. (Div. Pesticide Chem.), 194th Ann. Mtg., Chicago, Ill. The parameters mentioned for this process are a hydrogen pressure of 30-50 bar, Ni/kieselgur or Pd/carbon catalyst, and temperatures about 100.degree.-120.degree. C. The solvent used is NaOH in ethanol. Such a process requires extensive solvent processing and recycling. Accordingly, no industrial implementation of such a process is known.